In recent years, various types of information such as images and data, in addition to voice, are transmitted in radio communication, and in mobile communication, in particular. In the future, demands for still higher-speed transmission are expected to further increase, and carrying out high-speed transmission requires a radio transmission technique to use limited frequency resources more efficiently and realize higher-speed transmission efficiency.
One of radio transmission techniques capable of meeting such demands is OFDM (Orthogonal Frequency Division Multiplexing). OFDM is a multicarrier transmission technique for transmitting data in parallel using many subcarriers, has features such as high frequency efficiency, reduction of interference between symbols in a multipath environment and is known to be effective in improving transmission efficiency.
Discussions are underway to carry out frequency scheduling transmission and frequency diversity transmission when frequency-domain-multiplexing data to a plurality of radio communication mobile station apparatuses (hereinafter simply referred to as “mobile stations”) with a plurality of subcarriers using this OFDM on a downlink.
In frequency scheduling transmission, a radio communication base station apparatus (hereinafter simply referred to as “base station”) adaptively allocates subcarriers to each mobile station based on received quality per frequency band at each mobile station, and thereby obtain maximum multiuser diversity effect and carry out communication very efficiently. Such frequency scheduling transmission is a scheme suitable for mainly data communication or high-speed data communication when a mobile station is moving at a low speed. On the other hand, since frequency scheduling transmission requires feedback of received quality information from each mobile station, frequency scheduling transmission is unsuitable for data communication when the mobile station is moving at a high speed. Furthermore, frequency scheduling is normally performed per resource block (RB) formed into a block by grouping several neighboring subcarriers into a transmission time unit called “subframe.” The channel for carrying out such frequency scheduling transmission is called “localized channel” (hereinafter referred to as “Lch”).
By contrast, in the frequency diversity transmission, data for each mobile station is distributed across and allocated to subcarriers in the entire band, and high frequency diversity effect can therefore be obtained. Furthermore, frequency diversity transmission does not require received quality information from the mobile station, and therefore this is an effective scheme in the situation as described above in which it is difficult to apply frequency scheduling transmission. On the other hand, since frequency diversity transmission is carried out irrespective of the received quality at each mobile station, no multiuser diversity effect as in the case of frequency scheduling transmission is obtained. The channel for carrying out such frequency diversity transmission is called “Distributed Channel (hereinafter referred to as “Dch”).
Furthermore, frequency scheduling transmission through Lch and frequency diversity transmission through Dch may be carried out at the same time. That is, RBs used for Lch and RBs used for Dch on a plurality of subcarriers of one OFDM symbol may be frequency-domain-multiplexed. In this case, each RB and Lch are associated with each other and each RB and Dch are associated with each other in advance, and it is controlled in subframe units which RB should be used as Lch or Dch.
Furthermore, studies are being conducted to divide RBs to use for Dch into a plurality of subblocks and configure one Dch by a combination of different RB subblocks (e.g., see Non-Patent Document 1). To be more specific, when an RB is divided into two subblocks, one Dch is mapped to two divided subblocks.    Non-Patent Document 1: R1-072431 “Comparison between RB-level and Sub-carrier-level Distributed Transmission for Shared Data Channel in E-UTRA Downlink” 3GPP TSG RAN WG1 LTE Meeting, Kobe, Japan, 7-11 May 2007